AUT-2772: Add currentUrlMiddleware

The new language toggle middleware requires a currentUrl property
to be added to res.locals. This commit introduces the property along
with associated tests to verify that it is being set as expected.

src/middleware/current-url-middleware.ts

@@ -0,0 +1,13 @@
+import { NextFunction, Request, Response } from "express";
+
+export function setCurrentUrlMiddleware(
+  req: Request,
+  res: Response,
+  next: NextFunction,
+): void {
+
+  res.locals.currentUrl = new URL(
+    req.protocol + "://" + req.get("host") + req.originalUrl)
+
+  next();
+}

test/unit/middleware/current-url-middleware.test.ts

@@ -0,0 +1,49 @@
+import { expect } from "chai";
+import { describe } from "mocha";
+import { NextFunction, Request, Response } from "express";
+import { sinon } from "../../utils/test-utils";
+import { setCurrentUrlMiddleware } from "../../../src/middleware/current-url-middleware";
+import { mockRequest, mockResponse } from "mock-req-res";
+
+describe("currentUrl middleware", () => {
+  let req: Partial<Request>;
+  let res: Partial<Response>;
+  let next: NextFunction;
+
+  const originalUrl = '/sign-in-or-create?lng=cy';
+  const host = 'signin.account.gov.uk'
+
+  beforeEach(() => {
+    req = mockRequest({
+      originalUrl,
+      get: sinon.stub().withArgs('host').returns(host)
+    });
+    res = mockResponse();
+    next = sinon.fake() as unknown as NextFunction;
+  });
+
+  afterEach(() => {
+    sinon.restore();
+  });
+
+  describe("setCurrentUrlMiddleware", () => {
+    it("should add currentUrl to request locals", () => {
+      setCurrentUrlMiddleware(req as Request, res as Response, next);
+
+      expect(res.locals).to.have.property("currentUrl");
+    });
+
+    it("currentUrl should contain the scheme, host and originalUrl", () => {
+      setCurrentUrlMiddleware(req as Request, res as Response, next);
+      const currentUrlAsString = String(res.locals.currentUrl)
+
+      expect(currentUrlAsString).to.eq(`https://${host}${originalUrl}`);
+    });
+
+    it("should call next function", () => {
+      setCurrentUrlMiddleware(req as Request, res as Response, next);
+
+      expect(next).to.have.been.called;
+    });
+  });
+});